“Dexterous Magnetic Manipulation of Conductive Non-Magnetic Objects”, 2021-10-20 ():
Dexterous magnetic manipulation of ferromagnetic objects is well established, with 3 to 6° of freedom possible depending on object geometry1. There are objects for which non-contact dexterous manipulation is desirable that do not contain an appreciable amount of ferromagnetic material but do contain electrically conductive material.
Time-varying magnetic fields generate eddy currents in conductive materials, with resulting forces and torques due to the interaction of the eddy currents with the magnetic field. This phenomenon has previously been used to induce drag to reduce the motion of objects as they pass through a static field, or to apply force on an object in a single direction using a dynamic field, but has not been used to perform the type of dexterous manipulation of conductive objects that has been demonstrated with ferromagnetic objects.
Here we show that manipulation, with 6° of freedom, of conductive objects is possible by using multiple rotating magnetic dipole fields. Using dimensional analysis, combined with multiphysics numerical simulations and experimental verification, we characterize the forces and torques generated on a conductive sphere in a rotating magnetic dipole field.
With the resulting model, we perform dexterous manipulation in simulations and physical experiments.
Magnetic manipulation has the benefit of being contactless, which is particularly attractive when there is a risk of destructive collision between the manipulator and target. Such is the case with space debris, a considerable problem facing humanity owing to the Kessler syndrome. Most artificial space objects are fabricated primarily from aluminium, a non-magnetic but conductive material on which forces and torques can be generated by inducing eddy currents. The most commonly proposed application of this phenomenon is detumbling satellites by applying a static magnetic field to a rotating target. There exist numerical solutions for induced forces and/or torques on spinning solid and thin-walled spheres in uniform and non-uniform magnetic fields. An alternative method of detumbling satellites uses rotating Halbach arrays near the target. Rotating Halbach arrays have also been proposed as a means of traversing the exterior of the International Space Station (modelled as an infinite flat plate) using forces induced by eddy currents. This technique is similar to that used in eddy-current separation of non-magnetic materials. Methods based on eddy currents are distinct from those based on diamagnetism or ferrofluid environments, neither of which are applicable to manipulation of objects at a distance.
Here we show that dexterous manipulation of conductive objects is achievable using multiple static (in position) magnetic dipole-field sources capable of continuous dipole rotation about arbitrary axes. We demonstrate manipulation with 6° of freedom (6-DOF manipulation) in numerical microgravity simulations and 3-DOF manipulation in experimental microgravity simulations. This manipulation does not rely on dynamic motion of the conductive object itself; rather, the manipulation can be performed quasistatically. Both electromagnet and permanent-magnet devices have been developed to serve as field sources capable of generating continuously rotating magnetic dipole fields about arbitrary axes. Rotating magnetic dipole fields have been used previously to remotely actuate ferromagnetic devices that transduce the resulting magnetic torque into some form of rotational motion, such as micromachines and magnetic capsule endoscopes.